↦ z} { x ↦ y} = { x ↦ y, y ↦ z }. See also Substitution property in Equality (mathematics)#Some basic logical properties of equality First-order logic#Rules of inference Universal instantiation Lambda calculus#Substitution Truth-value semantics Unification (computer science) Metavariable Mutatis mutandis Rule of replacement Substitution (algebra) — about applying substitutions to polynoms and other algebraic expressions String interpolation — as seen in computer programming Notes Citations References Crabbé, M. (2004). On the Notion of Substitution. Logic Journal of the IGPL, 12, 111–124. Curry, H. B. (1952) On the definition of substitution, replacement and allied notions in an abstract formal system. Revue philosophique de Louvain 50, 251–269. Hunter, G. (1971). Metalogic: An Introduction to the Metatheory of Standard First Order Logic. University of California Press. Kleene, S. C. (1967). Mathematical Logic. Reprinted 2002, Dover. External links Propositional calculus Concepts in logic Logical truth Automated theorem proving Logic programming