Description: Substitution applied to an atomic wff. Version of equsb1 with a
disjoint variable condition, which neither requires ax-12 nor
ax-13 . (Contributed by NM, 10-May-1993)(Revised by BJ, 11-Sep-2019) Remove dependencies on axioms. (Revised by Wolf Lammen, 30-May-2023)(Proof shortened by Steven Nguyen, 19-Jun-2023) Revise
df-sb . (Revised by Steven Nguyen, 11-Jul-2023)(Proof shortened by Steven Nguyen, 22-Jul-2023)