Spending function overview
                        4.0: Spending function overview
Wang-Tsiatis Bounds     5.0: Wang-Tsiatis Bounds
checkScalar             6.0 Utility functions to verify variable
                        properties
gsBinomialExact         3.4: One-Sample Exact Binomial Boundary
                        Crossing Probabilities
gsBound                 2.6: Boundary derivation - low level
gsBoundCP               2.5: Conditional Power at Interim Boundaries
gsCP                    2.4: Conditional and Predictive Power, Overall
                        and Conditional Probability of Success
gsDensity               2.6: Group sequential design interim density
                        function
gsDesign                2.1: Design Derivation
gsDesign package overview
                        1.0 Group Sequential Design
gsProbability           2.2: Boundary Crossing Probabilities
nSurvival               3.4: Time-to-event sample size calculation
                        (Lachin-Foulkes)
normalGrid              3.1: Normal Density Grid
plot.gsDesign           2.3: Plots for group sequential designs
sfExponential           4.3: Exponential Spending Function
sfHSD                   4.1: Hwang-Shih-DeCani Spending Function
sfLDOF                  4.4: Lan-DeMets Spending function overview
sfLinear                4.6: Piecewise Linear Spending Function
sfLogistic              4.7: Two-parameter Spending Function Families
sfPoints                4.5: Pointwise Spending Function
sfPower                 4.2: Kim-DeMets (power) Spending Function
sfTDist                 4.8: t-distribution Spending Function
testBinomial            3.2: Testing, Confidence Intervals and Sample
                        Size for Comparing Two Binomial Rates
