Bijection Principle

Bijection Principle is a principle stating that an operator must bind one and only one variable, where 'variable' is defined as any locally A-bar bound NP.

Examples
This principle (BP for short) accounts for weak crossover violations, as in (i): (i) *Whoi does hisi mother admire ti (ii) Whoi ti likes hisi mother

Comments
The BP excludes the interpretation for (i) where both his and ti are bound variables bound by the operator who. The bound variable reading for the pronoun is allowed in (ii), since the pronoun, being locally A-bound by the trace of who, does not syntactically count as a variable.

Link
Utrecht Lexicon of Linguistics