assert("abs(13)=13", abs(13)=13)
assert("abs(-13)=13", abs(-13)=13)
assert("abs(13.0)=13.0", abs(13.0)=13.0)
assert("abs(-13.0)=13.0", abs(-13.0)=13.0)
assert("cos(0)=1", cos(0.0)=1.0)
assert("sin(0)=0", sin(0.0)=0.0)
assert("acos(1.0)=0", acos(1.0)=0.0)
assert("asin(0)=0",asin(0.0)=0.0)
assert("strrev",strreverse("abc")="cba")