The general principle for erasure operation, then, is this: 'a term X of the proper analysis can be used to erase a term Y of the proper analysis just in case the inherent part of the formative X is not distinct from the inherent part of the formative Y'.
- Chomsky (1969), a pag.182

[…] let us define an 'erasure transformation' as one that substitutes a term 'X' of its proper analysis for a term 'Y' of its proper analysis (leaving 'X' intact), and then deletes this new occurrence of 'X' which replaced 'Y' [...] an erasure operation can use the term 'X' to delete 'Y' just in case 'X' and 'Y' are identical.
- Chomsky (1969), a pag.145