Mary Heilmann’s solo exhibition “Highway, Oceans, Daydreams” featured paintings the eighty-one-year-old artist executed last spring and summer in her studio on Long Island’s East End during the Covid-19 lockdown, along with some earlier pieces for good measure. For five decades, Heilmann’s treatment of light, form, and space, frequently via a restricted palette, has been impressive. She tends to work within the easel tradition, and her surfaces—wood panels or stretched canvases—are modestly scaled. Thankfully, Heilmann has never received the memo that art has to be supersize and gratuitously