To-Do
 1. Fractions
+2. Tests
 3. expression as unit's val
+4. Revisar reduce y pasar a map
+5. mk :m recurse down primero
 6. Going multiprocess
 7. Functions! Derivate! Integrate!


import Exun.Pattern
import Exun
umatch "f * f'x", "cos(x)/sin(x)*ln(sin(x))"