one-character constructors?

[G.P.H. Josten]

# 
# Can anyone explain why:
# 
# ::Lift a =   Uu		// undefined value
# 	   | V a  	// defined value
# 
# is acceptable to the Clean compiler, but
# 
# ::Lift a =   U		// undefined value
# 	   | V a  	// defined value
# 
# is not?
# 
# thanks in advance for any help,
# 
# Matt.
# 

Sorry, U is a special thing, ask the Clean-team... Just don't use U as a 
constructor... Using a constructor with a name the same as one of the 
functions of the Std-libraries, gives trouble as well...

Geert