scala> def f(implicit x: Int) = println(x)
f: (implicit x: Int)Unit

scala> f
<console>:9: error: could not find implicit value for parameter x: Int
              f
              ^

scala> implicit val x1 = 3
x1: Int = 3

scala> f
3

scala> implicit val x2 = 4
x2: Int = 4

scala> f
<console>:11: error: ambiguous implicit values:
 both value x1 of type => Int
 and value x2 of type => Int
 match expected type Int
              f
              ^

scala>