added delcongs, Delcongs, unsafe_solver, safe_solver, FOL_basic_ss,
safe_asm_more_full_simp_tac
new addss (old version retained as unsafe_addss),
new auto_tac (old version retained as unsafe_auto_tac),
clasimpset with modification functions
Arith = FOL +
classes arith < term
consts "0" :: "'a::arith" ("0")
"1" :: "'a::arith" ("1")
"+" :: "['a::arith,'a] => 'a" (infixl 60)
end