This file proves that binding at the copy object is binding at one
reading: a token c-commands another in the copy object just when it
does in the reading in which the chains holding the second are read low. So the choice of copies
the semantic interface reads loses no binding relation, and the reading that shows a given relation
is found from the bound token alone. When nothing moves from itself a reading also creates no
binding, so binding at the copy object is binding at some
reading.
Implementation notes
The theorem names one reading as well as some reading because the reading is found locally, and
the step-by-step induction needs that: the test that a copy holds y is independent of the stage.
Without DistinctDaughters a reading may bind where the copy object does not: an object that
moves from itself, read low, comes to c-command the sister of its movement node.
Two chains sharing a mark could have mark reach copies with different terms, which MarksName
excludes. Reading each chain high or low is enough because the theorem concerns one pair of tokens
at a time.
Binding at the copy object is binding at the reading in which the chains holding the bound token
are read low, in a derivation of Merge steps that merges no token twice and moves no trace, when
marks name chains, the copy object has no traces and nothing moves from itself.