Removed a bunch of unused imports.

src/rules/derivatives.py

-from itertools import combinations
-
 from .utils import find_variables
 from .logarithmic import ln
 from .goniometry import sin, cos

src/rules/fractions.py

 from itertools import combinations, product
 
 from .utils import least_common_multiple, partition
-from ..node import ExpressionLeaf as L, Scope, negate, OP_DIV, OP_ADD, \
-        OP_MUL, OP_POW, nary_node, negate
+from ..node import ExpressionLeaf as L, Scope, OP_DIV, OP_ADD, OP_MUL, \
+        OP_POW, nary_node, negate
 from ..possibilities import Possibility as P, MESSAGES
 from ..translate import _
 

src/rules/goniometry.py

-from .utils import is_fraction
-from ..node import ExpressionNode as N, ExpressionLeaf as L, Scope, OP_ADD, \
-        OP_POW, OP_MUL, OP_DIV, OP_SIN, OP_COS, OP_TAN, OP_SQRT, PI, \
-        TYPE_OPERATOR
+from ..node import ExpressionNode as N, ExpressionLeaf as L, OP_ADD, OP_MUL, \
+        OP_DIV, OP_SIN, OP_COS, OP_TAN, OP_SQRT, PI, TYPE_OPERATOR
 from ..possibilities import Possibility as P, MESSAGES
 from ..translate import _
 

src/rules/numerics.py

@@ -99,7 +99,6 @@ def match_divide_numerics(node):
     assert node.is_op(OP_DIV)
 
     n, d = node
-    divide = False
     nv, dv = n.value, d.value
 
     if n.is_int() and d.is_int():

src/rules/sort.py

-from itertools import product, combinations
-
-from ..node import Scope, OP_ADD, OP_MUL
+from ..node import Scope, OP_MUL
 from ..possibilities import Possibility as P, MESSAGES
 from ..translate import _