Answer by taking a quote from the following article:

John Milton Cage Jr. (September 5, 1912 - August 12, 1992) was an American composer and music theorist. A pioneer of indeterminacy in music, electroacoustic music, and non-standard use of musical instruments, Cage was one of the leading figures of the post-war avant-garde. Critics have lauded him as one of the most influential composers of the 20th century. He was also instrumental in the development of modern dance, mostly through his association with choreographer Merce Cunningham, who was also Cage's romantic partner for most of their lives.

Cage's work from the sixties features some of his largest and most ambitious, not to mention socially utopian pieces, reflecting the mood of the era yet also his absorption of the writings of both Marshall McLuhan, on the effects of new media, and R. Buckminster Fuller, on the power of technology to promote social change. HPSCHD (1969), a gargantuan and long-running multimedia work made in collaboration with Lejaren Hiller, incorporated the mass superimposition of seven harpsichords playing chance-determined excerpts from the works of Cage, Hiller, and a potted history of canonical classics, with fifty-two tapes of computer-generated sounds, 6,400 slides of designs, many supplied by NASA, and shown from sixty-four slide projectors, with forty motion-picture films. The piece was initially rendered in a five-hour performance at the University of Illinois in 1969, in which the audience arrived after the piece had begun and left before it ended, wandering freely around the auditorium in the time for which they were there. Also in 1969, Cage produced the first fully notated work in years: Cheap Imitation for piano. The piece is a chance-controlled reworking of Erik Satie's Socrate, and, as both listeners and Cage himself noted, openly sympathetic to its source. Although Cage's affection for Satie's music was well-known, it was highly unusual for him to compose a personal work, one in which the composer is present. When asked about this apparent contradiction, Cage replied: "Obviously, Cheap Imitation lies outside of what may seem necessary in my work in general, and that's disturbing. I'm the first to be disturbed by it." Cage's fondness for the piece resulted in a recording--a rare occurrence, since Cage disliked making recordings of his music--made in 1976. Overall, Cheap Imitation marked a major change in Cage's music: he turned again to writing fully notated works for traditional instruments, and tried out several new approaches, such as improvisation, which he previously discouraged, but was able to use in works from the 1970s, such as Child of Tree (1975). Cheap Imitation became the last work Cage performed in public himself. Arthritis had troubled Cage since 1960, and by the early 1970s his hands were painfully swollen and rendered him unable to perform. Nevertheless, he still played Cheap Imitation during the 1970s, before finally having to give up performing. Preparing manuscripts also became difficult: before, published versions of pieces were done in Cage's calligraphic script; now, manuscripts for publication had to be completed by assistants. Matters were complicated further by David Tudor's departure from performing, which happened in early 1970s. Tudor decided to concentrate on composition instead, and so Cage, for the first time in two decades, had to start relying on commissions from other performers, and their respective abilities. Such performers included Grete Sultan, Paul Zukofsky, Margaret Leng Tan, and many others. Aside from music, Cage continued writing books of prose and poetry (mesostics). M was first published by Wesleyan University Press in 1973. In January 1978 Cage was invited by Kathan Brown of Crown Point Press to engage in printmaking, and Cage would go on to produce series of prints every year until his death; these, together with some late watercolors, constitute the largest portion of his extant visual art. In 1979 Cage's Empty Words was first published by Wesleyan University Press.

Did he work with any other composers in this period of his life?
Such performers included Grete Sultan, Paul Zukofsky, Margaret Leng Tan, and many others.