gf-3.1.6: examples/mathtext/MathTextGer.gf

concrete MathTextGer of MathText = LogicGer ** MathTextI with
  (LexLogic = LexLogicGer),
  (Syntax = SyntaxGer),
  (Lang = LangGer), ---- for ImpP3
  (Symbolic = SymbolicGer) ;