Left panel: primordial power spectrum inferred for minimum-variance unbiased estimator formalism. Dark blue curves show the estimate (our case A) for the primordial power spectrum assuming we cross-correlate only the 21 cm signal and the CMB; the solid blue line is for the diagonal approximation, while the dotted line uses full kernel inversion. Errors bands are for the 1 − σ Fisher information estimate. Red curves show the primordial power spectrum inferred when including foreground contaminants (case B) for both the diagonal approximation (solid) and full inversion (dashed). The solid cyan line is the input Planck primordial power spectrum (21cmFAST convention, proportional to ﹩{k}^{{n}_{s}}﹩). Right panel: Fisher estimate of the 1σ noise of the primordial power spectrum. Case A is the blue dashed line, while case B is the solid black line. Colored lines (red to green) show cases where no CMB cross-correlations are used but foregrounds are included at varying levels of foreground residual (ϵ = 1 for full foreground autopower to 0 for full foreground removal).