Interchangeable and Selfsame

adjective

• Mathematics, logic. ( such that the arguments or roles can be interchanged)
  • usage: "the arguments of the symmetric relation, `is a sister of,' are interchangeable"
• Capable of replacing or changing places with something else; permitting mutual substitution without loss of function or suitability.
  • usage: "interchangeable electric outlets" "interchangeable parts"
  • synonyms: exchangeable, similar, standardized, standardised

• (a.) Admitting of exchange or mutual substitution.
• (a.) Following each other in alternate succession; as, the four interchangeable seasons.

adjective

• Being the exact same one; not any other:.
  • usage: "this is the identical room we stayed in before"; "the themes of his stories are one and the same"; "saw the selfsame quotation in two newspapers"; "on this very spot"; "the very thing he said yesterday"; "the very man I want to see"
  • synonyms: identical, very