revise solution to Problem 1 in Problem Set 3.

Add 'EOF' as a token in the grammar.

Augmented are the following 2 files:

	src/calculator/Parser.java
	src/calculator/Type.java

Thank you!
							Lawrence X. Amlord
							  Oct 18th, 2014
							   Xi'an, China
add solution to Problem 2 in Problem Set 3.

Augmented is the following file:

	src/calculator/Lexer.java

Besides, additional 2 files are included:

	src/calculator/LexerTest.java
	src/calculator/SyntaxErrorException.java

Thank you!
							Lawrence X. Amlord
							  Oct 18th, 2014
							   Xi'an, China
initialize Problem Set 4: Building a Sudoku Solver with SAT.

Included are the following 29 files:

	.classpath
	.project
	samples/sudoku_4x4.txt
	samples/sudoku_easy.txt
	samples/sudoku_easy2.txt
	samples/sudoku_evil.txt
	samples/sudoku_hard.txt
	samples/sudoku_hard2.txt
	src/immutable/EmptyImList.java
	src/immutable/ImList.java
	src/immutable/ImListIterator.java
	src/immutable/ImListMap.java
	src/immutable/ImMap.java
	src/immutable/NonEmptyImList.java
	src/sat/SATSolver.java
	src/sat/SATSolverTest.java
	src/sat/env/Bool.java
	src/sat/env/Environment.java
	src/sat/env/Variable.java
	src/sat/formula/Clause.java
	src/sat/formula/ClauseTest.java
	src/sat/formula/Formula.java
	src/sat/formula/FormulaTest.java
	src/sat/formula/Literal.java
	src/sat/formula/NegLiteral.java
	src/sat/formula/PosLiteral.java
	src/sudoku/Main.java
	src/sudoku/Sudoku.java
	src/sudoku/SudokuTest.java

Thank you!
							Lawrence X. Amlord
							  Oct. 23th, 2014
							   Xi'an, China
fix mistakes in spec for constructor of Sudoku object.

Modified is the following file:

	src/sudoku/Sudoku.java

The formula dim*dim == square.length == square[i].length
is hold for 0 <= i < (dim^2 - 1), rather than 0<=i<dim.

Thank you!
							Lawrence X. Amlord
							  Oct. 23th, 2014
							   Xi'an, China