reconstruct missing pattern term

fixes #1137.

```
the definition of __<__ is not complete
the defining formula group is:
  1. forall x : Nat . 0 < suc(x)
  2. forall x, y : Nat . x < y => suc(x) < suc(y)
missing pattern for: __<__(0, 0)
missing pattern for: __<__(suc(_), 0)

the definition of f is not complete
the defining formula group is:
  1. forall x, y : Nat . f(x, suc(y)) = 0
  2. forall x, y : Nat . f(suc(x), y) = suc(0)
  3. forall x : Nat . f(suc(suc(x)), 0) = x
missing pattern for: f(0, 0)

the definition of f is not complete
the defining formula group is:
  1. forall x, y : Nat . f(x, suc(y), 0) = 0
  2. forall x, y, z : Nat . f(suc(x), suc(y), suc(z)) = suc(0)
missing pattern for: f(0, 0, _)
missing pattern for: f(0, suc(_), suc(_))
missing pattern for: f(suc(_), 0, _)
```