code: def _tchelper(tc_deps,evals,deps):
  	
  	for e in evals:
  		if e in tc_deps: # we've already included it
  			continue
  		else:
  			if e in deps: # has additional dependnecies
  				tc_deps[e]=deps[e]
  				# add to tc_deps the dependencies of the dependencies
  				_tchelper(tc_deps,deps[e],deps)
  	return tc_deps
docs: modifies graph in place