Completed some items from TODO list:

- Fraction term cancellation now has priority over constant multiplication.
- Some other issues had already been resolved.

TODO

@@ -59,43 +59,6 @@ Division of 0 by 1 reduces to 0.
  - validation: preorder traversal implementatie vergelijken met andere
                implementaties.
 
- - Fix the following loop using strategy (reduce_fraction_constants):
-   >>> 2 / 7 - 4 / 11
-   2 / 7 - 4 / 11
-   >>> @
-   22 / 77 - 28 / 77
-   >>> @
-   2 / 7 - 28 / 77
-   >>> @
-   2 / 7 + 4 / 11
-
- - Cancel terms before multiplying constants: (3 * ...) / (3 * ...) -> ... / ...
-    >>> (7/3)*(3/5)
-    7 / 3 * (3 / 5)
-    >>> ??
-    Expand fraction with nominator greater than denominator 7 / 3 to an integer
-    plus a fraction.
-    Multiply fractions 7 / 3 and 3 / 5.
-    >>> @
-    7 * 3 / (3 * 5)
-    >>> ?
-    Multiply constant 7 with 3.
-    >>> @
-    21 / (3 * 5)
-    >>> @
-    21 / 15
-    >>> @
-    7 / 5
-
- - Fix error while parsing unicode PI:
-   >>> sin(1/2 * pi)
-   sin(1 / 2 * π)
-   >>> @
-   unknown char � ignored.
-   unknown char � ignored.
-   ERROR: 41.7-41.8: "syntax error, unexpected TIMES" near "*".
-   ERROR: 41.14-41.15: "syntax error, unexpected RPAREN" near ")".
-
  - No matches for sin(pi), sin(2pi), sin(4pi), etc...
 
  - Create unit tests for node inequivalence operator.
@@ -112,11 +75,9 @@ Division of 0 by 1 reduces to 0.
 
  - Use pretty-print for expressions in hint messages.
 
- - Parser:
-   + add unit tests for operator associativity (derivatives/integrals).
+ - Parser: add unit tests for operator associativity (derivatives/integrals).
 
  - Modules:
    + Equations with substitution
-   + Sqrt
    + Sort
    + Gonio

src/rules/precedences.py

@@ -7,7 +7,7 @@ from .logarithmic import factor_in_exponent_multiplicant, \
 from .derivatives import chain_rule
 from .negation import double_negation, negated_factor, negated_nominator, \
         negated_denominator, negated_zero, negated_factor
-from .fractions import multiply_with_fraction
+from .fractions import multiply_with_fraction, extract_fraction_terms
 from .integrals import factor_out_constant, integrate_variable_root
 from .powers import remove_power_of_one
 from .sqrt import quadrant_sqrt, extract_sqrt_mult_priority
@@ -56,6 +56,9 @@ RELATIVE = [
 
         # sqrt(2 ^ 2)  ->  2  # not sqrt 4
         (quadrant_sqrt, raise_numerics),
+
+        #
+        (extract_fraction_terms, multiply_numerics),
         ]
 
 

tests/test_leiden_oefenopgave.py

@@ -173,8 +173,8 @@ class TestLeidenOefenopgave(TestCase):
         self.assertRewrite([
             '(7/3)(3/5)',
             '(7 * 3) / (3 * 5)',
-            '21 / (3 * 5)',
-            '21 / 15',
+            '3 / 3 * 7 / 5',
+            '1 * 7 / 5',
             '7 / 5',
         ])