The Holy Spirit who Proceeds from the Father

97. In  teaching  about  the  Person  of  the  Holy  Spirit,  the  Fathers  of  the  Church emphasize first and foremost what differentiates the Person of the Holy Spirit from the Persons of the Father and the Son, that is, that the Holy Spirit proceeds (in Ukrainian, iskhodyt; in Greek, exporeutai) from the Father. In conciliar unified fashion, they professed this belief through the Symbol of Faith: “I believe ... in the Holy Spirit, the Lord, the Giver of life, who proceeds from the Father.” On the procession of the Holy Spirit, Saint Cyril of Alexandria teaches: “The Holy Spirit is the  one  [who]  ...  pours  forth  from  God  the  Father,  through  the  Son,  and shows to us his existence, in the image of breath of the mouth” (Cyril of Alexandria, Dialogues on the Holy and Consubstantial Trinity, 2)
98. The  Holy  Fathers  made  a  distinction  between  the  interior  life  of  the  Most Holy Trinity and the revelation of the Trinity in creation. In the Most Holy Trinity, the Holy Spirit proceeds (in Ukrainian, iskhodyt; in Greek, exporeutai) from  the  Father—the  one  and  only  Source  of  the  Most Holy Trinity. When the Holy Fathers spoke about the action of the  Persons  of  the  Trinity  in  creation,  they  professed  that  the  Father  sends the Holy Spirit “through the Son”(See Gregory of Nyssa, On the Life of Saint Gregory the Wonderworker). Saint Cyril of Alexandria, professing this very same faith, explained this sending of the Holy Spirit “through  the  Son”  as  the  fact  that  the  Holy  Spirit  “comes  from  (in Ukrainian, походит; in Greek, προεναι) the Father and the Son” (See Cyril of Alexandria, Thesaurus on the Holy and Consubstantial Trinity) This interpretation was emphasized by the Fathers of the Council of Florence: “Some [were] saying the Holy Spirit comes from the Father and the Son, others saying the Holy Spirit comes from the Father through the  Son.  All  were  aiming  at  the  same  meaning  in  different  words”(Council of Florence, Bull Laetentur caeli [Let the Heavens Rejoice] ( July 6, 1439)). This opinion was also expressed in the Articles of the Union of Brest: “The Holy Spirit ... proceeds from one Source, as if from a well-spring, from the Father, through the Son”(Articles of the Union of Brest, 1).

From Christ Our Pascha, 

the Catechism of the Ukrainian Catholic Church