user: 下面的汇编指令对应的C源代码是什么：

```asm
<possible_trees_aux>:
  endbr64
  push   %r15
  mov    $0x1,%eax
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x88,%rsp
  mov    %rdi,0x38(%rsp)
  mov    %rsi,0x48(%rsp)
  cmp    %rsi,%rdi
  jae    L462
  lea    0x1(%rdi),%rax
  movl   $0x0,0x7c(%rsp)
  mov    %rax,0x18(%rsp)
  mov    0x18(%rsp),%rax
  movl   $0x1,0x78(%rsp)
  cmp    %rax,0x48(%rsp)
  je     L609
L73:
  add    $0x1,%rax
  movl   $0x0,0x6c(%rsp)
  mov    %rax,0x70(%rsp)
  mov    %rax,%r15
  movl   $0x1,0x68(%rsp)
  cmp    %r15,0x48(%rsp)
  je     L764
L886:
  lea    0x1(%r15),%rax
  movl   $0x0,0x5c(%rsp)
  mov    %rax,0x10(%rsp)
  mov    0x10(%rsp),%rdx
  mov    %rax,0x60(%rsp)
  mov    0x48(%rsp),%rax
  movl   $0x1,0x58(%rsp)
  cmp    %rdx,%rax
  je     L316
L369:
  add    $0x1,%rdx
  mov    %r15,0x40(%rsp)
  mov    %rax,%r15
  mov    %rdx,%r13
  mov    %rdx,0x50(%rsp)
  movl   $0x0,0x30(%rsp)
  movl   $0x1,0x20(%rsp)
  cmp    %r13,%r15
  je     L247
L347:
  lea    0x1(%r13),%rax
  movl   $0x0,0xc(%rsp)
  mov    $0x1,%ebp
  mov    %rax,0x28(%rsp)
  mov    %rax,%r12
L220:
  mov    %r15,%rsi
  mov    %r12,%rdi
  call   <possible_trees_aux>
  imul   %ebp,%eax
  add    %eax,0xc(%rsp)
  cmp    %r12,%r15
  je     L223
  cmp    %r12,%r13
  jae    L72
  mov    %r13,%r14
  xor    %ebp,%ebp
L174:
  mov    %r14,%rsi
  mov    %r13,%rdi
  add    $0x1,%r14
  call   <possible_trees_aux>
  mov    %r12,%rsi
  mov    %r14,%rdi
  mov    %eax,%ebx
  call   <possible_trees_aux>
  imul   %eax,%ebx
  add    %ebx,%ebp
  cmp    %r12,%r14
  jb     L174
  add    $0x1,%r12
  jmp    L220
  nopl   (%rax)
L223:
  mov    0xc(%rsp),%r14d
  imul   0x20(%rsp),%r14d
  add    %r14d,0x30(%rsp)
  mov    0x10(%rsp),%r14
  cmp    %r13,%r14
  jae    L192
  mov    %r14,%rbp
  xor    %r12d,%r12d
L748:
  mov    %rbp,%rsi
  mov    %r14,%rdi
  add    $0x1,%rbp
  call   <possible_trees_aux>
  mov    %r13,%rsi
  mov    %rbp,%rdi
  mov    %eax,%ebx
  call   <possible_trees_aux>
  imul   %eax,%ebx
  add    %ebx,%r12d
  cmp    %r13,%rbp
  jb     L748
  mov    %r12d,0x20(%rsp)
L565:
  mov    0x28(%rsp),%r13
  cmp    %r13,%r15
  jne    L347
L247:
  mov    0x20(%rsp),%eax
  mov    0x40(%rsp),%r15
  add    0x30(%rsp),%eax
  imul   0x58(%rsp),%eax
  add    %eax,0x5c(%rsp)
  cmp    0x10(%rsp),%r15
  jae    L380
  movl   $0x0,0x28(%rsp)
  mov    %r15,%r13
  mov    $0x1,%ebx
L201:
  mov    0x10(%rsp),%rax
  add    $0x1,%r13
  cmp    %rax,%r13
  jae    L549
L674:
  mov    %ebx,0xc(%rsp)
  mov    %r13,%r12
  xor    %r14d,%r14d
  mov    %rax,%rbx
L457:
  mov    %r12,%rsi
  mov    %r13,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %rbx,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%r14d
  cmp    %rbx,%r12
  jb     L457
  mov    0xc(%rsp),%ebx
  imul   %ebx,%r14d
  add    %r14d,0x28(%rsp)
  cmp    %r15,%r13
  jbe    L197
  movl   $0x0,0xc(%rsp)
  mov    $0x1,%ebx
  mov    %r15,%r14
L536:
  add    $0x1,%r14
  cmp    %r14,%r13
  jbe    L424
L126:
  xor    %ecx,%ecx
  mov    %ebx,0x20(%rsp)
  mov    %r14,%r12
  mov    %r14,%rbx
  mov    %ecx,%r14d
L64:
  mov    %r12,%rsi
  mov    %rbx,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r13,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%r14d
  cmp    %r12,%r13
  ja     L64
  mov    %r14d,%ecx
  mov    %rbx,%r14
  mov    0x20(%rsp),%ebx
  imul   %ebx,%ecx
  add    %ecx,0xc(%rsp)
  cmp    %r15,%r14
  jbe    L237
  mov    %r15,%r12
  xor    %ebx,%ebx
L843:
  mov    %r12,%rsi
  mov    %r15,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r14,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%ebx
  cmp    %r12,%r14
  ja     L843
  add    $0x1,%r14
  cmp    %r14,%r13
  ja     L126
L424:
  mov    0x10(%rsp),%rax
  add    $0x1,%r13
  add    0xc(%rsp),%ebx
  cmp    %rax,%r13
  jb     L674
L549:
  add    0x28(%rsp),%ebx
  mov    %ebx,0x58(%rsp)
L600:
  mov    0x50(%rsp),%rax
  mov    %rax,0x10(%rsp)
  mov    0x48(%rsp),%rax
  mov    0x10(%rsp),%rdx
  cmp    %rdx,%rax
  jne    L369
L316:
  mov    0x58(%rsp),%eax
  add    0x5c(%rsp),%eax
  imul   0x68(%rsp),%eax
  add    %eax,0x6c(%rsp)
  mov    0x18(%rsp),%rax
  cmp    %r15,%rax
  jae    L300
  movl   $0x0,0x50(%rsp)
  mov    %rax,%r14
  movl   $0x1,0x40(%rsp)
  mov    %r15,0x30(%rsp)
L458:
  add    $0x1,%r14
  cmp    0x30(%rsp),%r14
  jae    L140
L408:
  movl   $0x0,0x58(%rsp)
  mov    %r14,%r13
  movl   $0x1,0x28(%rsp)
  mov    %r14,0x10(%rsp)
L754:
  mov    0x30(%rsp),%r15
  add    $0x1,%r13
  cmp    %r15,%r13
  jae    L601
L23:
  movl   $0x0,0xc(%rsp)
  mov    $0x1,%ebx
  mov    %r13,%r14
L664:
  add    $0x1,%r14
  cmp    %r15,%r14
  jae    L694
L31:
  xor    %ecx,%ecx
  mov    %ebx,0x20(%rsp)
  mov    %r14,%r12
  mov    %r14,%rbx
  mov    %ecx,%r14d
L681:
  mov    %r12,%rsi
  mov    %rbx,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r15,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%r14d
  cmp    %r15,%r12
  jb     L681
  mov    %r14d,%ecx
  mov    %rbx,%r14
  mov    0x20(%rsp),%ebx
  imul   %ebx,%ecx
  add    %ecx,0xc(%rsp)
  cmp    %r14,%r13
  jae    L357
  mov    %r13,%r12
  xor    %ebx,%ebx
L303:
  mov    %r12,%rsi
  mov    %r13,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r14,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%ebx
  cmp    %r12,%r14
  ja     L303
  add    $0x1,%r14
  cmp    %r15,%r14
  jb     L31
L694:
  mov    0x10(%rsp),%r12
  add    0xc(%rsp),%ebx
  imul   0x28(%rsp),%ebx
  add    %ebx,0x58(%rsp)
  cmp    %r13,%r12
  jae    L299
  movl   $0x0,0xc(%rsp)
  mov    $0x1,%ebx
  mov    %r12,%r15
L319:
  add    $0x1,%r15
  cmp    %r15,%r13
  jbe    L647
L283:
  mov    %r15,%r12
  xor    %r14d,%r14d
L966:
  mov    %r12,%rsi
  mov    %r15,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r13,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%r14d
  cmp    %r12,%r13
  ja     L966
  mov    0x10(%rsp),%rax
  mov    %r14d,%ecx
  imul   %ebx,%ecx
  add    %ecx,0xc(%rsp)
  cmp    %r15,%rax
  jae    L484
  mov    %rax,%r12
  xor    %ebx,%ebx
  mov    %rax,%r14
L576:
  mov    %r12,%rsi
  mov    %r14,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r15,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%ebx
  cmp    %r12,%r15
  ja     L576
  add    $0x1,%r15
  cmp    %r15,%r13
  ja     L283
L647:
  mov    0x30(%rsp),%r15
  add    0xc(%rsp),%ebx
  add    $0x1,%r13
  mov    %ebx,0x28(%rsp)
  cmp    %r15,%r13
  jb     L23
L601:
  mov    0x10(%rsp),%r14
  mov    0x18(%rsp),%r12
  mov    0x58(%rsp),%eax
  add    0x28(%rsp),%eax
  imul   0x40(%rsp),%eax
  add    %eax,0x50(%rsp)
  cmp    %r12,%r14
  jbe    L323
  movl   $0x0,0xc(%rsp)
  mov    $0x1,%ebx
  mov    %r12,%r15
L24:
  add    $0x1,%r15
  cmp    %r15,%r14
  jbe    L846
L895:
  mov    %r15,%r12
  xor    %r13d,%r13d
L446:
  mov    %r12,%rsi
  mov    %r15,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r14,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%r13d
  cmp    %r12,%r14
  ja     L446
  mov    %r13d,%ecx
  mov    0x18(%rsp),%r13
  imul   %ebx,%ecx
  add    %ecx,0xc(%rsp)
  cmp    %r13,%r15
  jbe    L320
  mov    %r13,%r12
  xor    %ebx,%ebx
L308:
  mov    %r12,%rsi
  mov    %r13,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r15,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%ebx
  cmp    %r12,%r15
  ja     L308
  add    $0x1,%r15
  cmp    %r15,%r14
  ja     L895
L846:
  add    0xc(%rsp),%ebx
  add    $0x1,%r14
  mov    %ebx,0x40(%rsp)
  cmp    0x30(%rsp),%r14
  jb     L408
L140:
  mov    0x40(%rsp),%eax
  add    0x50(%rsp),%eax
  mov    %eax,0x68(%rsp)
L875:
  mov    0x60(%rsp),%r15
  cmp    %r15,0x48(%rsp)
  jne    L886
L764:
  mov    0x68(%rsp),%eax
  mov    0x18(%rsp),%rdx
  add    0x6c(%rsp),%eax
  imul   0x78(%rsp),%eax
  add    %eax,0x7c(%rsp)
  mov    0x38(%rsp),%rax
  cmp    %rdx,%rax
  jae    L152
  mov    %rax,0x20(%rsp)
  movl   $0x0,0x50(%rsp)
  movl   $0x1,0x40(%rsp)
L262:
  addq   $0x1,0x20(%rsp)
  mov    0x20(%rsp),%r15
  cmp    0x18(%rsp),%r15
  jae    L428
  movl   $0x0,0x58(%rsp)
  movl   $0x1,0x30(%rsp)
L630:
  add    $0x1,%r15
  cmp    0x18(%rsp),%r15
  jae    L96
L132:
  movl   $0x0,0x28(%rsp)
  mov    %r15,%r13
  mov    $0x1,%ebx
L544:
  mov    0x18(%rsp),%rax
  add    $0x1,%r13
  cmp    %rax,%r13
  jae    L153
L12:
  mov    %ebx,0xc(%rsp)
  mov    %r13,%r12
  xor    %r14d,%r14d
  mov    %rax,%rbx
L233:
  mov    %r12,%rsi
  mov    %r13,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %rbx,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%r14d
  cmp    %rbx,%r12
  jb     L233
  mov    0xc(%rsp),%ebx
  imul   %ebx,%r14d
  add    %r14d,0x28(%rsp)
  cmp    %r13,%r15
  jae    L1006
  movl   $0x0,0xc(%rsp)
  mov    $0x1,%ebx
  mov    %r15,%r14
L768:
  add    $0x1,%r14
  cmp    %r14,%r13
  jbe    L90
L25:
  xor    %ecx,%ecx
  mov    %ebx,0x10(%rsp)
  mov    %r14,%r12
  mov    %r14,%rbx
  mov    %ecx,%r14d
L560:
  mov    %r12,%rsi
  mov    %rbx,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r13,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%r14d
  cmp    %r12,%r13
  ja     L560
  mov    %r14d,%ecx
  mov    %rbx,%r14
  mov    0x10(%rsp),%ebx
  imul   %ebx,%ecx
  add    %ecx,0xc(%rsp)
  cmp    %r14,%r15
  jae    L960
  mov    %r15,%r12
  xor    %ebx,%ebx
L599:
  mov    %r12,%rsi
  mov    %r15,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r14,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%ebx
  cmp    %r12,%r14
  ja     L599
  add    $0x1,%r14
  cmp    %r14,%r13
  ja     L25
L90:
  mov    0x18(%rsp),%rax
  add    $0x1,%r13
  add    0xc(%rsp),%ebx
  cmp    %rax,%r13
  jb     L12
L153:
  mov    0x20(%rsp),%r12
  add    0x28(%rsp),%ebx
  imul   0x30(%rsp),%ebx
  add    %ebx,0x58(%rsp)
  cmp    %r15,%r12
  jae    L672
  movl   $0x0,0xc(%rsp)
  mov    $0x1,%ebx
  mov    %r12,%r14
L975:
  add    $0x1,%r14
  cmp    %r14,%r15
  jbe    L638
L416:
  mov    %r14,%r12
  xor    %r13d,%r13d
L274:
  mov    %r12,%rsi
  mov    %r14,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r15,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%r13d
  cmp    %r12,%r15
  ja     L274
  mov    0x20(%rsp),%rax
  mov    %r13d,%ecx
  imul   %ebx,%ecx
  add    %ecx,0xc(%rsp)
  cmp    %r14,%rax
  jae    L730
  mov    %rax,%r12
  xor    %ebx,%ebx
  mov    %rax,%r13
L429:
  mov    %r12,%rsi
  mov    %r13,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r14,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%ebx
  cmp    %r12,%r14
  ja     L429
  add    $0x1,%r14
  cmp    %r14,%r15
  ja     L416
L638:
  add    0xc(%rsp),%ebx
  add    $0x1,%r15
  mov    %ebx,0x30(%rsp)
  cmp    0x18(%rsp),%r15
  jb     L132
L96:
  mov    0x30(%rsp),%eax
  mov    0x38(%rsp),%r13
  add    0x58(%rsp),%eax
  imul   0x40(%rsp),%eax
  add    %eax,0x50(%rsp)
  mov    0x20(%rsp),%rax
  cmp    %rax,%r13
  jae    L735
  movl   $0x0,0x30(%rsp)
  movl   $0x1,0x28(%rsp)
L856:
  mov    0x20(%rsp),%r14
  add    $0x1,%r13
  cmp    %r13,%r14
  jbe    L726
L364:
  movl   $0x0,0xc(%rsp)
  mov    $0x1,%ebx
  mov    %r13,%r15
L619:
  add    $0x1,%r15
  cmp    %r15,%r14
  jbe    L387
L398:
  xor    %ecx,%ecx
  mov    %ebx,0x10(%rsp)
  mov    %r15,%r12
  mov    %r15,%rbx
  mov    %ecx,%r15d
L582:
  mov    %r12,%rsi
  mov    %rbx,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r14,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%r15d
  cmp    %r12,%r14
  ja     L582
  mov    %r15d,%ecx
  mov    %rbx,%r15
  mov    0x10(%rsp),%ebx
  imul   %ebx,%ecx
  add    %ecx,0xc(%rsp)
  cmp    %r15,%r13
  jae    L818
  mov    %r13,%r12
  xor    %ebx,%ebx
L795:
  mov    %r12,%rsi
  mov    %r13,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r15,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%ebx
  cmp    %r12,%r15
  ja     L795
  add    $0x1,%r15
  cmp    %r15,%r14
  ja     L398
L387:
  mov    0x38(%rsp),%r12
  add    0xc(%rsp),%ebx
  imul   0x28(%rsp),%ebx
  add    %ebx,0x30(%rsp)
  cmp    %r13,%r12
  jae    L543
  movl   $0x0,0xc(%rsp)
  mov    $0x1,%ebx
  mov    %r12,%r14
L682:
  add    $0x1,%r14
  cmp    %r14,%r13
  jbe    L956
L180:
  mov    %r14,%r12
  xor    %r15d,%r15d
L853:
  mov    %r12,%rsi
  mov    %r14,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r13,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%r15d
  cmp    %r12,%r13
  ja     L853
  mov    %r15d,%ecx
  mov    0x38(%rsp),%r15
  imul   %ebx,%ecx
  add    %ecx,0xc(%rsp)
  cmp    %r14,%r15
  jae    L157
  mov    %r15,%r12
  xor    %ebx,%ebx
L951:
  mov    %r12,%rsi
  mov    %r15,%rdi
  add    $0x1,%r12
  call   <possible_trees_aux>
  mov    %r14,%rsi
  mov    %r12,%rdi
  mov    %eax,%ebp
  call   <possible_trees_aux>
  imul   %eax,%ebp
  add    %ebp,%ebx
  cmp    %r12,%r14
  ja     L951
  add    $0x1,%r14
  cmp    %r14,%r13
  ja     L180
L956:
  mov    0x20(%rsp),%r14
  add    0xc(%rsp),%ebx
  add    $0x1,%r13
  mov    %ebx,0x28(%rsp)
  cmp    %r13,%r14
  ja     L364
L726:
  mov    0x28(%rsp),%eax
  add    0x30(%rsp),%eax
  mov    %eax,0x40(%rsp)
  jmp    L262
  nopw   0x0(%rax,%rax,1)
L237:
  mov    $0x1,%ebx
  jmp    L536
  nopw   0x0(%rax,%rax,1)
L72:
  mov    $0x1,%ebp
  add    $0x1,%r12
  jmp    L220
  xchg   %ax,%ax
L357:
  mov    $0x1,%ebx
  jmp    L664
  nopw   0x0(%rax,%rax,1)
L484:
  mov    $0x1,%ebx
  jmp    L319
  nopw   0x0(%rax,%rax,1)
L299:
  movl   $0x1,0x28(%rsp)
  jmp    L754
  nopl   (%rax)
L320:
  mov    $0x1,%ebx
  jmp    L24
  nopw   0x0(%rax,%rax,1)
L197:
  mov    $0x1,%ebx
  jmp    L201
  nopw   0x0(%rax,%rax,1)
L192:
  movl   $0x1,0x20(%rsp)
  jmp    L565
  nopl   (%rax)
L960:
  mov    $0x1,%ebx
  jmp    L768
  nopw   0x0(%rax,%rax,1)
L730:
  mov    $0x1,%ebx
  jmp    L975
  nopw   0x0(%rax,%rax,1)
L1006:
  mov    $0x1,%ebx
  jmp    L544
  nopw   0x0(%rax,%rax,1)
L157:
  mov    $0x1,%ebx
  jmp    L682
  nopw   0x0(%rax,%rax,1)
L818:
  mov    $0x1,%ebx
  jmp    L619
L380:
  movl   $0x1,0x58(%rsp)
  jmp    L600
L323:
  movl   $0x1,0x40(%rsp)
  jmp    L458
L428:
  mov    0x40(%rsp),%eax
  add    0x50(%rsp),%eax
  mov    %eax,0x78(%rsp)
L49:
  mov    0x70(%rsp),%rax
  mov    %rax,0x18(%rsp)
  mov    0x18(%rsp),%rax
  cmp    %rax,0x48(%rsp)
  jne    L73
L609:
  mov    0x78(%rsp),%eax
  add    0x7c(%rsp),%eax
L462:
  add    $0x88,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L543:
  movl   $0x1,0x28(%rsp)
  jmp    L856
L672:
  movl   $0x1,0x30(%rsp)
  jmp    L630
L300:
  movl   $0x1,0x68(%rsp)
  jmp    L875
L735:
  movl   $0x1,0x40(%rsp)
  jmp    L262
L152:
  movl   $0x1,0x78(%rsp)
  jmp    L49
```

assistant: ```c
unsigned possible_trees_aux(size_t begin, size_t end) {
  if (begin >= end) {
    return 1;
  }
  unsigned res = 0;
  size_t i;
  for (i = begin; i < end; i++) {
    res += possible_trees_aux(begin, i) * possible_trees_aux(i + 1, end);
  }
  return res;
}
```