procedure. For example, when inferring the type ?α of λx , abs x , Lean would perform the following schematic type derivation: Cst x : ?β ⊢⊢⊢ abs : ?β → ?γ Var x : ?β ⊢⊢⊢ x : ?β App x : ?β ⊢⊢⊢ abs x : convenient alternative to option.catch ma ma’, Lean supports the syn- tax ma.catch ma’. Here is a schematic example that demonstrates throwing and catching with this syntax: do { . . ., if . . . then option

terms that are checked independently by the kernel. 8.1 Pattern Matching The interpretation of schematic patterns is the first step of the compilation process. We have seen that the cases_on recursor can