HOUSTON—The meeting that started the trouble took place at a monastery in Florence, Ariz.

Under a gazebo's shade, a Ukrainian physicist who aspires to be a monk met with a Milwaukee lawyer seven years ago and began planning a firm whose profits from rapid-fire stock trades would go mostly to charity. They and another founder eventually named it SXP Analytics LLC after St. Xenia, an 18th century Russian who gave the poor her possessions.

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