encode "fequal" reasoning rules in Metis problem, just as is done for Sledgehammer -- otherwise any proof that relies on "fequal" found by Sledgehammer can't be reconstructed
Arith = FOL +
classes arith < term
consts "0" :: "'a::arith" ("0")
"1" :: "'a::arith" ("1")
"+" :: "['a::arith,'a] => 'a" (infixl 60)
end