sclass OneColorTheoryChecker {

  replace Cell with URecognizer.Cell.

  replace Theory with BodyOfEvidence<S>.

  new ProbabilisticScheduler scheduler;

  record OneColorTheory(S text, Cell cell, RGB color) > Theory {

    toString {

      ret renderProbabilityGuess() + ": " + dollarVarsMeanFields(text, this);

    }

    selfType branch(O... _) { this; }

  }

  // create the theory object and initiate the reasoning

  // you have to step the scheduler afterwards to get results

  OneColorTheory makeTheory(Cell cell) {

    var color = cell.averageColor();

    var theory = new OneColorTheory("Color of every pixel in $cell is $color.", cell, color);

    testOneColorTheory(cell, theory);

    ret theory;

  }

  void noteCellColor(Cell cell, OneColorTheory theory) {

    var desc = "Pixel check at " + cell;

    if (theory.hasEvidenceFromSource(desc)) return;

    var strength = doubleRatio(cell.area(), theory.cell.area()); // how much do we have to say about the cell in the theory?

    var p = colorDistanceToProbability(cell.averageColor(), theory.color);

    addExampleToTheory(theory, desc, p, strength);

  }

  double colorDistanceToProbability(RGB col1, RGB col2) {

    double sim = colorSimilarity(col1, col2), sqr = sqr(sim);

    printFunctionCall colorDistanceToProbability(+col1, +col2, +sim, +sqr);

    ret sqr;

  }

  void testOneColorTheory(Cell cell, OneColorTheory theory) {  

    noteCellColor(cell, theory);

    scheduler.atRelative(dontZoomTooFar(cell), r {

      for (var split : usefulSplits(cell))

        scheduler.atRelative(split.probability(), r {

          for (var cell : split!)

            testOneColorTheory(cell, theory.branch(description := "recursion to " + cell));

        });

    });

  }

  L<WithProbability<Cell[]>> usefulSplits(Cell cell) {

    ret map withProbability1(llNonNulls(cell.split(0, 2), cell.split(1, 2)));

  }

  // probability penalty .25 for zooming in 3 steps

  double dontZoomTooFar(Cell cell) {

    ret 0.75;

  }

  void addExampleToTheory(Theory theory, S desc, double probabilityOfTheory, double strengthOfEvidence) {

    theory.addEvidence(desc, probabilityOfTheory, /* scheduler.currentProbability()* */ strengthOfEvidence);

  }

}