The generalized Cartan-Hadamard conjecture says that if Ω is a domain with fixed volume in a complete, simply connected Riemannian n-manifold M with sectional curvature K κ 0, then ∂ Ω has the least possible boundary volume when Ω is a round n-ball with constant curvature K = κ. The case n = 2 and κ = 0 is an old result of Weil. We give a unified proof of this conjecture in dimensions n = 2 and n = 4 when κ = 0, and a special case of the conjecture for κ < 0 and a version for κ > 0. Our argument uses a new interpretation, based on optical transport, optimal transport, and linear programming, of Croke's proof for n = 4 and κ = 0. The generalization to n = 4 and κ = 0 is a new result. As Croke implicitly did, we relax the curvature condition K κ to a weaker candle condition Candle(κ) or LCD(κ).We also find counterexamples to a naïve version of the Cartan-Hadamard conjecture: For every ε > 0, there is a Riemannian Ω ∼ = B 3 with (1 − ε)-pinched negative curvature, and with |∂ Ω| bounded by a function of ε and |Ω| arbitrarily large.We begin with a pointwise isoperimetric problem called "the problem of the Little Prince." Its proof becomes part of the more general method.