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diff --git a/src/core.rs b/src/core.rs
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+// Copyright (c) 2018 The predicates-rs Project Developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use crate::reflection;
+
+/// Trait for generically evaluating a type against a dynamically created
+/// predicate function.
+///
+/// The exact meaning of `eval` depends on the situation, but will usually
+/// mean that the evaluated item is in some sort of pre-defined set.  This is
+/// different from `Ord` and `Eq` in that an `item` will almost never be the
+/// same type as the implementing `Predicate` type.
+pub trait Predicate<Item: ?Sized>: reflection::PredicateReflection {
+    /// Execute this `Predicate` against `variable`, returning the resulting
+    /// boolean.
+    fn eval(&self, variable: &Item) -> bool;
+
+    /// Find a case that proves this predicate as `expected` when run against `variable`.
+    fn find_case<'a>(&'a self, expected: bool, variable: &Item) -> Option<reflection::Case<'a>> {
+        let actual = self.eval(variable);
+        if expected == actual {
+            Some(reflection::Case::new(None, actual))
+        } else {
+            None
+        }
+    }
+}