Change name convention for creating Lean expressions

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add theorems Truth, EqMP and EqTElim

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add add_theorem

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Prove congr1, congr2 and congr theorems. Add xtrans theorem.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add Eta axiom

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Fix bug in is_convertible

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Define Lean forall. Prove forall elimination.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Add more theorems

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>