| Description: Extend wff definition to
include atomic formulas using the equality
     predicate.
 
     (Instead of introducing weq 1643 as an axiomatic statement, as was done in an
     older version of this database, we introduce it by "proving" a
special
     case of set theory's more general wceq 1642.  This lets us avoid overloading
     the   connective,
thus preventing ambiguity that would complicate
     certain Metamath parsers.  However, logically weq 1643 is
considered to be a
     primitive syntax, even though here it is artificially "derived"
from
     wceq 1642.  Note:  To see the proof steps of this
syntax proof, type "show
     proof weq /all" in the Metamath program.)  (Contributed by NM,
     24-Jan-2006.)  |