var et4 errorTest4
	et4.Error() // ok, not an error method.
	var et5 errorTest5
	et5.error() // ok, not an error method.
	// Interfaces can be used with any verb.
	var iface interface {
		ToTheMadness() bool // Method ToTheMadness usually returns false
	}
	fmt.Printf("%f", iface) // ok: fmt treats interfaces as transparent and iface may well have a float concrete type
	// Can't print a function.