Relational projection (clip + compact)

SYNOPSIS

    #(signature)

OPTIONS

    #(summarized_options)

DESCRIPTION

This operator projects tuples on attributes whose names are specified in 
ATTRIBUTES. Unlike SQL, this operator **always** removes duplicates in the
result so that the output is a set of tuples, that is, a relation.

With the allbut option, the operator projects ATTRIBUTES away instead of 
keeping them. 

EXAMPLE

    # What are supplier cities ?
    !(alf project suppliers -- city)

    # What are all but supplier's id and name
    !(alf project --allbut suppliers -- sid name)