#;2> (define-class <a> ())
#;3> (define b (make <a>))
#;4> 
#;4> (define-method (foo (c <a>))
--->   (print "foo v1 on " c))

Note: implicitly defining generic-procedure: foo
#t
#;5> 
#;5> (define-method (foo (c <a>))
--->   (print "foo v2 on " c))
#t
#;6> (foo b)
foo v2 on #<coops instance of `<a>'>
#;7>