t:Term. s(t) 
Termt:Term. f(t) Termt,r:Term. t/r Term| Who Cites s? | |
| s | Def s(t) == f(t)/q(f(t)) |
| Thm* t:Term. s(t) Term | |
| f | Def f(t) == SUBX(q(t); SUBX(X; Q(X))) |
| Thm* t:Term. f(t) Term | |
| subx | Def t/e == t[e/X] |
| Thm* t,r:Term. t/r Term |
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