TR10i watches for sqrt(3)f + g -> 2(cos(pi/6)f + sin(pi/6)g)
TR5 and TR6 only target f**2 (helper can do all f**(2**m)
CTRstrat uses count_ops, too
correct CTR4 def; add induced formula for cos(x)+sin(x)
fix _TR56; make CTR2 a rule list
correct TR10i for when there is a gcd on induceable pair
exprtools
rework trig sum detection