CS 61A Structure and Interpretation of Computer Programs Python Variance Hypergeometric Geometric Poisson Normal Approximation Chebyshev Indicators Random Variables Expectation Symmetry Conditional Probability Bayes' Rule Counting Multinomial Coefficient Binomial Poisson Approximation Hypergeometric Sampling 2026 Happy new year Trees Mutability Iterators Sequences Containers Data Abstraction Recursion Tree Recursion Higher-Order Functions Functions Control Enjoyable Adventure Silicon Valley San Francisco Bay Area Berkeley