slice_lhs a b { tac }
zooms to the left hand side, uses associativity for categorical
composition as needed, zooms in on the a
-th through b
-th morphisms, and invokes tac
.
slice_rhs a b { tac }
zooms to the right hand side, uses associativity for categorical
composition as needed, zooms in on the a
-th through b
-th morphisms, and invokes tac
.