Frederick Hammersley's "Insist Upon #5" from 1987 presents a refined example of the artist's late geometric work, in which precise formal relationships are held in quiet but unmistakable tension. Executed in oil on panel at an intimate 20.3 by 16.5 centimeters, the work rewards close looking, its modest scale concentrating the visual logic into something nearly aphoristic. Hammersley, a key figure in the California Hard Edge movement and a participant in the landmark 1959 exhibition "Four Abstract Classicists," brought to his paintings a deeply personal approach to geometry, one rooted in intuition as much as structure. The title itself reflects a characteristic habit: Hammersley famously titled his works through wordplay and private association, so that "Insist Upon #5" carries a sense of conviction embedded directly in the nomenclature. The panel support, a consistent choice throughout his mature practice, lends the surface a taut, unforgiving quality that heightens the precision of each edge and the density of each color field. Where canvas might soften the boundary between forms, panel holds Hammersley's compositions accountable, making every decision visible and permanent. Signed by the artist, this work enters the market through Addison Rowe Gallery and represents a compelling opportunity for collectors drawn to postwar American abstraction at a scale suited to intimate domestic or institutional display. Works of this period demonstrate Hammersley's sustained commitment to a vision that resisted both the theatricality of Abstract Expressionism and the industrial remove of later Minimalism, occupying instead a singular, warmly rigorous space of its own.