= y == x = y
t,x:Term. (t = x) 
Prop= y == x t & x = y tt:(u Term), x:u. (t = x) Propt,x:Term. (t = x) Propt,r:Term. SUBX(t; r) Term| Some definitions of interest. | |
| repst | Def x = y == x = y |
| Thm* t,x:Term. (t = x) Prop | |
| reps | Def x = y == x t & x = y t |
| Thm* t:(u Term), x:u. (t = x) Prop | |
| Thm* t,x:Term. (t = x) Prop | |
| subx | Def SUBX(t; e) == t[e/X] |
| Thm* t,r:Term. SUBX(t; r) Term |
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