Added the first goniometry rewrite rule.

src/rules/goniometry.py

+from ..node import ExpressionNode as N, ExpressionLeaf as L, Scope, \
+        OP_ADD, OP_POW, OP_MUL, OP_SIN, OP_COS, OP_TAN
+from ..possibilities import Possibility as P, MESSAGES
+from ..translate import _
+
+
+def match_add_quadrants(node):
+    """
+    sin(x) ^ 2 + cos(x) ^ 2  ->  1
+    """
+    assert node.is_op(OP_ADD)
+
+    p = []
+    sin_q, cos_q = node
+
+    if sin_q.is_power(2) and cos_q.is_power(2):
+        sin, cos = sin_q[0], cos_q[0]
+
+        if sin.is_op(OP_SIN) and cos.is_op(OP_COS):
+            p.append(P(node, add_quadrants, ()))
+
+    return p
+
+
+def add_quadrants(root, args):
+    """
+    sin(x) ^ 2 + cos(x) ^ 2  ->  1
+    """
+    return L(1)
+
+
+MESSAGES[add_quadrants] = _('Add the sinus and cosinus quadrants to 1.')

tests/test_rules_goniometry.py

+from src.rules.goniometry import match_add_quadrants, add_quadrants
+from src.possibilities import Possibility as P
+from tests.rulestestcase import RulesTestCase, tree
+
+
+class TestRulesGoniometry(RulesTestCase):
+
+    def test_match_add_quadrants(self):
+        root = tree('sin(x) ^ 2 + cos(x) ^ 2')
+        possibilities = match_add_quadrants(root)
+        self.assertEqualPos(possibilities, [P(root, add_quadrants, ())])
+
+    def test_add_quadrants(self):
+        root = tree('sin(x) ^ 2 + cos(x) ^ 2')
+        self.assertEqual(add_quadrants(root, ()), 1)