type-subtraction.scala

scala> trait A { val a: String = "this is A" }
defined trait A

scala> trait B { val b: String = "this is B" }
defined trait B

scala> trait C { val c: String = "this is C" }
defined trait C

scala> val abc = new A with B with C
abc: A with B with C = $anon$1@786ff1cb

scala> abc.a
res0: String = this is A

scala> abc.b
res1: String = this is B

scala> abc.c
res2: String = this is C

scala> def onlyAB(ab: A with B): A with B = ab
onlyAB: (ab: A with B)A with B

scala> val ab = onlyAB(abc)
ab: A with B = $anon$1@786ff1cb

scala> ab.c
            ^
       error: value c is not a member of A with B

scala> ab.a
res5: String = this is A

scala> ab.b
res6: String = this is B