The infinitive is like a substantive herein:
a. It may be the subject or object of a verb.
b. With the (neuter) article it shows all the case forms (except the vocative): τὸ (τοῦ, τῷ, τὸ) λύ_ειν, λύ_σειν, etc.
c. It may be governed by prepositions: πρὸ τοῦ λύ_ειν.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].