Lambek Invariants of Commutative Squares in a Homological Category

We consider the Lambek invariants (introduced by Joachim Lambek in 1964) in the context of semiexact and homological categories in the sense of Grandis. We generalize the Lambek isomorphism theorem to semiexact and homological categories. Throughout the text, for completeness we give proofs of some lemmas which are known in the additive case for the case of semiexact and homological categories.